Austenitin

Austenitin is a phase of iron-carbon alloys, commonly known as austenite. It is a solid solution of carbon in gamma-iron (γ-Fe), which has a face-centered cubic (FCC) crystal structure. This phase is stable at elevated temperatures, typically between approximately 727 °C and 1538 °C, depending on the carbon content. At room temperature, pure iron's stable form is ferrite (alpha-iron), which has a body-centered cubic (BCC) structure.

Austenite is a crucial phase in the heat treatment of steel. Its FCC structure allows for a higher solubility of carbon compared to ferrite. This increased solubility is vital for processes like quenching, where steel is rapidly cooled from the austenitic state to form martensite, a very hard and brittle phase. Subsequent tempering of martensite allows for a controlled reduction in hardness and an increase in toughness, forming various steel microstructures.

The presence of alloying elements can significantly affect the temperature range of austenite stability. For example, nickel and manganese are known austenite stabilizers, meaning they can extend the temperature range in which austenite is stable, even down to room temperature in some cases, leading to stainless steels like the austenitic grades. Conversely, elements like chromium and molybdenum are ferrite stabilizers. Understanding the phase diagram of iron-carbon and alloyed steels is fundamental to controlling their mechanical properties through heat treatment.